Each oculist, optometrist, or optician practicing his profession shall pay the following license tax: in cities or towns of over 5,000 inhabitants, $25; in cities and towns of 1,000 to 5,000 inhabitants, $10; and all other places, whether incorporated or not, $5, but no license shall be paid to the county. If such business is conducted as a firm or as a corporation in which more than one person is engaged, each oculist, optometrist, or optician so engaged shall pay the license as above stated; provided, that the license imposed by this section shall not apply until such oculist, optometrist, or optician shall have practiced his profession as long as two years. A licensee having procured a license in the city or town where he has his principal office may practice his profession in any other place without the payment of an additional license.